When processing semiconductor workpieces or substrates into integrated circuits, excited gas plasmas are often used. For example sputter etching uses a plasma to remove a layer of unwanted material from the substrate surface, while sputter deposition uses a plasma and a target of material to deposit a layer onto the substrate.
The process of sputter etching is generally known and utilizes the ionized particles of a charged gas plasma to bombard the surface of a substrate and dislodge or "sputter" away substrate particles from the surface of the substrate. In sputter etching, a plasma gas is introduced into a processing chamber which is preferably vacuum sealed and which is typically fabricated from quartz, ceramic or another suitable dielectric material. The substrate to be sputter etched is supported on an electrically charged base or electrode within the processing chamber whereon the substrate develops an electrical charge or bias. The plasma gas is introduced into the vacuum chamber opposite the surface of the charged substrate, and energy is coupled to the gas, such as by using an induction coil which surrounds the quartz processing chamber and inductively couples energy through the processing chamber walls. The energy from the induced electric field ionizes the gas particles to form the plasma or plasma cloud which includes particles having a net charge opposite in polarity to the charge of the biased substrate. The ionized particles in the plasma are attracted to the substrate surface, bombarding the surface and dislodging or etching material particles from the substrate.
In sputter deposition, a biased target of material is positioned in the processing chamber generally opposite the substrate. The plasma particles bombard the biased target and dislodge particles of target material which then deposit on the substrate to form a material layer.
Plasma processing is accompanied by the generation of undesired contaminant particles. Particle generation may be due to the plasma chemistry, arcing within the plasma or the processing chamber, and/or the accumulation and peeling of the deposits from surfaces within the processing chamber. Further contaminant particles are created during the plasma etching and plasma sputter deposition processes. The contaminant particles are usually suspended within the generated plasma during processing. However, upon removal of the energy from the plasma and the subsequent extinguishing of the plasma, the contaminant particles are released and some of the particles condense on the surface of the substrate thereby resulting in irreversible particle contamination of the substrate. Particle contamination constitutes one of the major yield limitations in plasma processing of Very Large Scale Integration (VLSI) devices.
It is an objective of the present invention to increase the yield of plasma processes such as plasma etching and plasma sputter deposition of VLSI devices.
Accordingly, it is an objective of the present invention to reduce particle contamination during plasma processing.
Furthermore, it is an objective to prevent released contaminant particles from condensing on the surface of a substrate when a plasma is extinguished.